How to Grow Bog Onion

This unusual woodland curiosity is very low maintenance

Jack in the Pulpit
KenWiedemann / Getty Images

Bog onion is a great choice for native-plant shade gardens in the eastern United States. It is one of the more unusual native plants that you can grow and is very low-maintenance. Bog onion is a plant that fascinates children and the young at heart, a plant not difficult to picture in a fairyland setting.

Although slow-growing bog onion plants flower in spring, it is primarily the spathe, a hooded, cup-like growth or spadix that forms an erect spike. The actual flowers are contained on the spadix, but they are not showy; it is the spathe that you notice from a distance in spring, especially when it is striped and/or tinged with purple. Three subspecies exist, and there can be quite a bit of variation in coloration. The top of the spathe is a lip that curls over the spadix as if forming a roof.

By fall, some mature plants will also offer a cluster of showy red berries. They become more visible after the spathe withers away. The berries shine brightly and will add considerable luster to your shade garden late in the growing season.

Bog onion plants look good when surrounded by a mass of low-growing ground covers such as impatient Lucy (Impatiens walleriana). In fact, when bog onion plants go dormant and leave a hole in your shade garden in mid-summer, plug some impatient Lucy into the vacant spaces to fill them up again. Plant bog onion corms or seedlings in the spring.

Botanical Name Arisaema triphyllum
Common Name Bog onion, Jack-in-the-pulpit, wake robin
Plant Type Herbaceous corm
Mature Size 1-2 ft. tall, with a similar spread
Sun Exposure Partial shade to full shade
Soil Type Moist, humusy
Soil pH Acidic
Bloom Time April to May
Flower Color Greenish-purple
Hardiness Zones 4-9 (USDA)
Native Area Eastern North America
Toxicity Toxic to people and pets

Bog Onion Care

Bog onion needs shade, an adequate water supply, and nutrients. Once these three elements are provided, the plant is not a lot of work to grow.

To plant, make a 6-inch hole in the ground in fall and drop in the corm, as you would do if you were planting a crocus. Once the plants have come up in spring and put on some size, shovel 2 to 3 inches of mulch around them in order to conserve moisture.

The three-part compound leaf of bog onion may remind some of poison ivy (Toxicodendron radicans) at certain stages of the latter's growth (remember, "leaflets three, let it be"). The leaf structure also resembles that of trillium which shares bog onions native habitat, as well as the nickname, "wake robin."

Light

Some shade is an absolute must. The plant performs well even in deep shade. Grow bog onion plants in shade gardens and/or woodland gardens.

Soil

These wildflowers do not demand the superb drainage that many plants do, making them an option for boggy soils. The idea is to mimic the native habitat, which is damp, acidic areas of the forest rich in organic matter.

Water

Evenly moist soil is another must for growing bog onion.

Temperature and Humidity

Because it likes boggy conditions—hence the name bog onion—these plants do well in moist conditions, where it doesn't get too hot or too cold.

Fertilizer

Fertilizing with compost is sufficient in many cases. But use a fertilizer containing ammonium-N if your soil pH is not acidic enough.

Bog Onion Varieties

  • 'Arisaema consanguineum': has purplish with light green stripes, ending in a long "tongue" that makes it look like a cobra's head
  • 'Arisaema saxatile': has a long tongue but in this case, the tongue is the spadix and the spathe and is white
  • 'Arisaema griffithii': offers an elaborate light-green veining pattern at the top

How to Grow Bog Onion From Seed

Bog onion seeds need to be cold stratified to germinate. This means keeping them damp in sphagnum moss, in your fridge, for at least 60 days. Then, plant in a soilless potting medium and keep in a cool, damp place. Germination should take two to three weeks; Seedlings should remain indoors for two years.

Common Pests and Diseases

While not a destination for most pests and diseases, the bog onion is a favorite for slugs. This is easily remedied by placing a small dish of beer in your garden, and letting the slugs crawl in for a drink.